In high elevation community type receiving stations, which are currently in wide use, close in mobile transmitters, operating outside of a predetermined desirable communication frequency may cause undue interference with desired communication transmitters because of intermodulation distortion. While receiver selectivity can compensate for and even obviate this problem in some cases, it is desirable to somehow minimize the very high signal levels from adjacent channels when a nearby mobile transmitter would otherwise come through the selectivity skirt of the receiver.